Our genomes are DNA-based. Retroviruses are viruses with RNA-based genomes that, once they’ve infected a cell, create a DNA copy of their genome that they insert into the genome of their host. That’s us, in the case of human endogenous retroviruses, or HERVs.

Endo = within.

HERVs are found within our genomes. They have become part of us, they’re replicated and passed onto our children along with the rest of our DNA. To be passed on through generations, the virus had to have infected our germ cells sometime in the past.

Almost all ERVs no longer function as viruses because they are only remnants or are repressed.

Dogs have ERVs, too. The authors of the research I’m covering here have called them CfERVs: Canis familiaris ERVs. Canis are the dogs – wolves, coyotes, jackals included. familiaris is the one we know well. *Woof* 🙂

The dog genome–from a female boxer, for what it’s worth–was examined for ERVs by a Swedish group of scientists lead by Göran Andersson. It turns out that dogs have about one-sixth of the number of ERVs than humans do, suggesting dogs are better at suppressing or eliminating them than we are.[2]

One group of CfERVs looked similar to a HERV, a human ERV (HERV-Fc). Could this have been shared between dogs and humans over the 10,000-odd years they’ve been hanging out together? The authors write in their abstract:

A novel group of gammaretrovirus-like CfERV with high similarity to HERV-Fc1 was found to have potential for active retrotransposition and possibly lateral transmissions between dog and human as a result of close interactions during at least 10.000 years.

10,000 years is a blink of time when you’re thinking about evolution. Active retroviruses evolve very fast, but once they become endogenous–become part of the host genome–they ought to change at the same mutation rate as the other genes of the host, which isn’t all that fast.

I have to admit I’m nonplussed by the reference to 10,000 years–an estimate of how long dogs have been domesticated–in the abstract and discussion of the paper, as the estimates of the age of the common ancestors of the dog and human HERV-Fc that Göran’s team report within the body of their paper are much older, millions of years old. I’m left not knowing quite what to make of it. The thought that horizontal transfer of ERVs between humans and dogs might have occurred during the period of the domestication of dogs is nice (if a bit cosy), but you’d think their evidence tells them that have to look further back in the past.[3]

Either way, there are suggestions that an ERV previously found only within primates has been seen in dogs, so–in a sense–we share some ERVs with our dogs.

[2] I’m leaving out a bunch of interesting results about where ERVs are in the dog genome. They’re particularly interesting if you’re interested in epigenetics and genome structure as I am, but they’re part of another story as you can see.

[3] One probably equally questionable speculative idea might be that the ERVs were transferred between the ancestors of primates and dogs up whilst eating, with primates perhaps being the more likely meal than the dogs’ ancestors.

I’ve yet to read it (and I doubt I’ll find time soon, either!), but Druzhkova et al‘s PLoS One paperAncient DNA Analysis Affirms the Canid from Altai as a Primitive Dog may have something to contribute to the age of domestication of dogs. The abstract reads:

The origin of domestic dogs remains controversial, with genetic data indicating a separation between modern dogs and wolves in the Late Pleistocene. However, only a few dog-like fossils are found prior to the Last Glacial Maximum, and it is widely accepted that the dog domestication predates the beginning of agriculture about 10,000 years ago. In order to evaluate the genetic relationship of one of the oldest dogs, we have isolated ancient DNA from the recently described putative 33,000-year old Pleistocene dog from Altai and analysed 413 nucleotides of the mitochondrial control region. Our analyses reveal that the unique haplotype of the Altai dog is more closely related to modern dogs and prehistoric New World canids than it is to contemporary wolves. Further genetic analyses of ancient canids may reveal a more exact date and centre of domestication.

Code for Life is the blog of Dr Grant Jacobs who has wide-ranging interests in science-related subjects, especially genetics, bioinformatics and science communication. To learn more about Code for Life (topics, copyright, comments, writing), see the introductory page Twitter: @BioinfoTools

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